Wattmeter



4 Sheets-Sheet T. DUNCAN.

WATTMBTER (No Model.)

No. 573,078. Patented Dec. 15, 1896.

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4 SheetsSheet 2 T. DUNCAN.

WATTMETER.

No. 573,078. I Patented Dec. 15,1896.

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' (No Model.) 4 Sheets-Sheet 3.

T. DUNCAN. WATTMETER.

No. 573,078. Patented Dec. 15, 1896.

lnggemtoz (No Model.) 4 Sheets-Sheet 4.

T. DUNCAN.

WATTMBTER.

N0.'573,078. Patented Dec. 15, 1896.

(gm/mentor, flawed/5 3267266117? UNITED STATES PATENT GEEICE.

THOMAS DUNCAN, OF FORT VAYNE, INDIANA.

WATTMETER.

SPECIFICATION forming part of Letters Patent No. 573,078, dated December15, 1896.

Application filed April 29, 1896.

T0 at whom 2125 may concern:

Be it known that I, THOMAS DUNCAN, a citizen of the United States,residing at Fort \Va-yne, in the county of Allen and State of Indiana,have invented certain new and useful Improvements in \Vattmeters, ofwhich the following is a specification.

This invention relates to the construction and operation of integratingwattmeters for alternating electric currents, and pertains to that classknown as induction-motor meters, which are ordinarily made to consist ofa revoluble metallic body or armature actuated by the resulting fieldproduced by two other magnetic fields differing in phase.

The most important factor sought in the construction of a wattmetcr isaccuracy, or

that the rate of rotation shall at all times vary in exact ratio to thewatt energy being used, and the record coincide with a straight line.

A further desirable object is the evolution of a meter that shall not besusceptible to, or perceptibly affected by, changes in the rate ofalternations and that shall be accurate Within wide ranges ofelectromotive force.

To these ends the present invention is primarily addressed and itconsists,amon g other things, in combining with a closed-circuitarmature a field due to and varying with the current in amperes flowingin the series coils, an asynphased field representing the electromotiveforce in volts and varying directly as the pressure, and means forinducing an independent torque between said voltage field and armature,in combining with an armature, series coils, and shunt-coil means forcausing the shunt-coil to act independently upon the armature to inducea starting torque, and in various other novel features and details, ashereinafter pointed out and claimed.

In the drawings, Figure l is'a plan view, in horizontal section, throughthe field and shunt or volt coils and their cores and the armature of ameter embodying my invention. Fig. 2

is a front elevation of said meter; Fig. 3, a side elevation in verticalcentral section; Fig. 4, a detail of a modified or alternative form ofthe shunt or volt coil core-punching; Fig. 5, an enlarged detail insectional elevation, embracing the lower part of the spindle, itsadjustable step or bearing, and accessory de- Serial No. 589.611.(Nomad) vices. Figs. (5, 7, 8, and 9 are diagrams illustrating differentmethods of connecting in various circuits and systems of distribution;and Figs. 10 to 111 show diit'erentarran gements of the armature,volt-coil, and the armaturediverter for inducing the independentstarting torque and overcoming the friction on very small loads withlarge meters.

Referring to the drawings, A represents the base of the meter box orframe, reinforced by ribs a underneath and formed with inverted cups orsockets to, surrounding each bolt or screw hole, for the reception of afilling of wax or other sealing material a to prevent tampering, andwith a boss or leveling-table a at its front edge, planed off at rightangles to the axis of the spindle, so as to determine the trueverticality of the latter by the use of a small spirit-level.

A is the back of the frame rising from this base, and A an ovcrhan gin gbracketsupporting at its outer end the registering-train A inclosed in asuitable casing. Between the base A and the bracket A is mounted the vertical spindle l3, engaging and driving, by means of the worm Z) and intcrmeshing wormwheel, the registering-traii'i. The foot of this spindleis stepped in a jewel, sapphire, for instance, I), set into a movableblock B, resting upon a spring 0 which takes up shocks and preventsbreakin of the jewel if the meter is roughly used, both block and springbeing inclosed in and guided by a cylindrical socket in the upper end ofthe screw-threaded jewelpost B which is threaded through the base foradjustment and held firmly in any given adjustment by means of thejam-nut U, as shown, its head being sealed by wax, as above suggested.Upon the jewel-post is a liftingnut B adapted to be turned up againstsome projecting part carried on the spindle to lift the latter off ofthe jewel and jam it against the overhead bearing to prevent rotationwhen the meter is not being used or is in transit from one place toanother. The top of the spindle is held in position by the screwbearing1), threaded through the overhung bracket and tightened up by thejam-nut Z), which bears against a boss If from said bracket.

0 is the armature, consisting of a drum or cylinder of aluminium orother suitable metal,

forming a closed circuit, and secured to the spindle by means of a hub cand set-screw 0', so as to be adjustable lengthwise thereof, if desired,to vary the torque by moving it into or out of the field. At oppositesides of this armature are placed the field-coils D, connected in themain circuit in series or in multiple, depending upon the amount ofcurrent and the size of wire with which they are wound, so thatthecurrent supplying the lamps or other translating devices traverses them.These coils embrace a laminated fieldcore D of iron and of essentiallythe form shown, that is to say, having an elongated yoke (l and inturnedpoles d, upon which latter the coils are wound at opposite ends of adiameter through the armature and around an axis represented bysuchdiameter extended. This form of core possesses several advantageousfeatures. It reduces the mag netic resistance of the field of the coilsto the lowest possible amount, whereby the coils themselves may be madeto consist of very few turns and yet produce a dense field of magnetism.This at the same time keeps down the C R loss in said coils on accountof the length of wire being small. It also prevents the flux fromdiffusing and leaking from the coils and producing an irregular torque,but keeps it concentrated at the poles in an effective manner.

To further increase the efficiency of the field magnet, the insettingpoles or cores proper, d, are enlarged to present an area greater thanthat of the connecting-yoke between them, and advisably to about twicethe area of the yoke, or in about the proportion shown in the drawings.This will allow an amount of iron in the yoke always below magneticsaturation even when on full load. A less amount may cause an increasein reluctance and detract from the efiiciency, and a greater amount hasalso been experimentally demonstrated to reduce the beneficial results,the form and proportions above indicated always producing the very best,to wit, a speed varying in exact ratio to the power or watts. This isprobably due to the lines of force being more evenly diffused by theenlarged poles. The punchings building up this laminated core are heldtogether, and the core and coils supported upon the meterframe, byscrew-bolts (Z taking into lugs d", insetting from said frame at theproper height. The coils are connected with the outside current throughthe bind ing-posts D, fastened upon the insulating board or support D atthe back of the meter-box. To further guard against contact with theframe of the meter, insulating-pieces D provided with holes (1, areemployed, through which the inleading wires pass to make contact withthe binding-posts.

The shunt or volt coil E is also provided with a laminated iron core,upon one end only of which the coil is wound. If wound upon both ends,the proportion-of speed to load is very wavy and poor, due, presumably,to the following: A test being made with a coil on both ends the speedfell off considerably as the load increased instead of keeping on in astraight line, on account, probably, of the lines of force from thefieldcoils passing through the volt-core and developing a countereleetromotive force or pressure in the voltcoil, thereby causing it toreduce its field as the load increased around the series coils. Thisdetrimental effect is largely diminished by winding the coil upon oneend of the core only, even when the'core is the same size from end toend, but upon enlarging the unwound end, as shown in the drawings, itentirely disappears, the effect of enlarging this end being to cause thelines which previously leaked through the volt-core to pass straightthrough from one pole of the field-magnet to the other. In the moreeligible form of this improvement, therefore, the laminated volt orshunt core E has one end 6 enlarged, and upon the other reduced end 6the shuntcoil is wound. In this enlarged end core the punchings may havethe outline shown in Figs. 1 and 10 or that detailed in Fig. 4, whichlatter answers well. It follows that any intermediate form will attainthe object sought in approximately the highest degree, and in factalmost any form in which the free end or pole of the core or punching islarger than the end forming the core proper to the exciting or volt coilwill give beneficial results over and in addition to those attained bythe use of a uniform core also wound at one end only. This form of coreenables the production of a strong field of force with a minimum numberof turns; it gives the greatest self-induction, to wit, with straightcores, and it is a form which enables the meter to give a straight-linecharacteristic, due to its allowing the current in the shunt-coil tovary as the voltage. This sh u ntcoil and core are advisably mountedwith their axis at right angles or perpendicular to the axis of thefield-coils, or about so, and preferably within the armature, with theunwound or enlarged end toward the yoke of the core of the field-magnetand between the poles thereof and intersecting their magnetic axis. Forthis purpose a supporting-arm 1C is secured to the back of the meter-boxor frame by means of a screw-bolt e flwh ich passes through the yoke ofthe field-core and serves thereby as an additional means to bind thepunehings of the latter together and hold it firmly in position. To thefront end of said supporting-arm is soldered an upright tube or sleeveE, projecting both above and beneath the arm and loosely embracing themeter-spindle. The punchings, suitably apertured at a are driven ontothe upper reach or limb of the sleeve,which projects within the armatureto a tight fit, and to insure their proper positioning one side of thesleeve may be flattened and the aperture through the punchingscorrespondingly outlined, as in 'I ig. at, so that the edges of thesuperposed such nature that it will permit a flow of cur rent varyingwith the electromotive force. This resistance preferably consists of twocoils f, wound upon the parallel extension of a U-shaped core f, oflaminated iron, and it is conveniently fastened to the frame of themeter at the back, as in Fig. 3, by means of the screw-bolt F, passingthrough the yoke of the core, with the coils supported upon theupwardly-projecting limbs of said core.

Inductance-coils for lagging the currents in the shunt-circuits ofmeters have been used previous to this, but they have been ofa formwhich partook either of a closed magnetic circuit or one having a verysmall air-gap. Such forms are unsuited to the present purpose, sincethey will not permit a fiow of current to traverse them which will varywith the electromotive force, in which case the field produced by thevolt-coil would not respond in a constant ratio to the changes in theelectromotive force of the circuit. The U -shaped form, however,accomplishes the desired result. It has already been mentioned that thevol t-coil also possesses this quality, (of permit ting a fiow ofcurrent varying with the electromotive force,) and since it is connectedup in series with the described resistance-coil it follows that thefield representing the electromotive force in volts and acting upon thearmature must vary directly as the pressure. \Ve have, then, the fielddue to and varying with the current or amperes flowing in the seriesfield-coils and the field due to the current flowing in the shunt orvolt coil and varying with the electromotive force of the circuit, bothacting upon the aluminium armature and producing a torque equal to thepower or watts. Each of these fields, taken by itself, produces anoscillating magnetic field, the lines of which are at right angles tothe face of the coil. The two fields when taken together and being outof step or having asynchronous phases produce a resultant field whichrevolves or shifts around a vertical axis. The surface of the aluminiumcyl inder orv armature is therefore being continuously cut or threadedby lines of force as they sweep round. Currents are induced in thealuminium which, by Lenzs law, are in such directions as to resistmotion, and since the cylinder is freely suspended its endeavor toresist motion of the field results in its be-' ing setin motion itself.

In order to prevent acceleration and to keep the speed of the armatureproportional to the energy to be measured, a load or drag must beapplied, and one that will vary directly as the speed. To accomplishthis, it iscommon practice to employ a metallic disk driven between thepoles or one or more permanent magnets, which induce eddy currents inthe disk and exert a damping or braking force, which varies directly asthe speed, so that the resulting speed upon any load will be equal tothe watts. Herein the disk G is shown as secured upon the meter-spindleimmediately above the lifting-nut so that the latter when turned upengages with its hub and raises the spindle. The permanent magnets G aremade adjustable in order to obtain the proper rate of rotation byshifting their poles, being for this purpose mounted as to their lowerlimbs in clamps G each of which is held in adjusted position against thebase by a screw-bolt G entering one of the cups a and having its headsealedwith wax, so that by loosening the bolt the poles of the magnetmaybe set in or out with reference to the axis of the disk.

In the construction of meters in general it is common to employ aseparate or auxiliary winding on the series coils to overcome thefriction and inertia of starting, particularly in the case of largemeters. As to this the present improvement consists in establishing acondition wherein the volt or shunt coil acts independently upon thearmature in causing it to rotate in the same direction as that due tothe resultant of the series and shunt coils collectively. This result isobtained by placing in front of the shunt-coil and on the other side ofthe shell of the armature-cylinder a magnetizable pin or piece of ironwire II, hereinafter termed the diverter, whereby the lines of forceestablished by the coil pass through the cylinder to reach the pin andin so doing develop eddy currents in said cylinder. These currents, onaccount of their selfinduction, will lag behind the currents in thevolt-coil, an d will therefore present to the pole or core of said coila like sign of polarity, as shown in Fig. M at N and n, causing thecylinder to be moved or repelled around in the direction of the arrow,since a magnetic repulsion will exist between the poles of the samesign. This repulsion can be increased by adjusting the diverter-in thedirection of rotation. For this purpose it may be supported upon abracket-arm H, adj ustably secured upon the lower reach or limb of thesleeve IF, which supports the volt core and coil by means of a splitcollar 7t and bindingscrew it or other suitable means, so that byswinging the arm the diverter may be displaced laterally, and when theproper bal ancing effect has been secured may be held in fixed positionby tightening up the screw. To illustrate, Fig. 10 shows the diverter inline with the volt-coil, so that there is no tendency to repel thearmature to either side, but only in a line coincident with their axes,

which are the same. Therefore no torque will be exerted and no motion orlateral repulsion takes place. In Fig. 11 the volt-coil is removed fromwithin the armature to expose the means for adjusting the diverter. InFigs. 12 and 14 the diverter has been moved to the right to inducerotation of the cylinder in the direction indicated by the arrow, and asthe angle is increased the repulsive force inducing rotation is alsoincreased.

In Fig. 12 the diverter-pin is shown as threesided, so that in additionto, or independently of, adjusting the bracket-arm the pin itself may bemoved, that is, the sharp edge toward the cylinder may be slightlyturned one way or the other and effect a change in the rotation, and .inFig. 13 a horizontally-adj ustable pin 71? is set in the vertical pin IIfor fine adjustments, the set-screw 07. allowing a longitudinalmovement, the vertical pin a swinging or pivotal movement, and thebracket arm a lateral adjustment. This device can be used to advantagein supplying a want that it is impossible to meet in other meters nowupon the market, that is to say, the ability to change the startingtorque in a few seconds without having to take the meter from its placeof installation and without having to change any windings or resistancessimply by altering the position of the diverter, or, in other words,adjusting its position to the right or to the left. It is quite commonwith all meters that after they have been in operation for some timethey become sluggish or slow upon small loads, owing, probably, to theaccumulation of dust upon the moving parts or the oil becoming thick,when they have to be removed and cleaned. This is avoided by the presentconstruction.

Since the tendency to rotation due to the diverter derives its energysolely from the shuntfield, it is obviously at its maximum when the loadis first turned on and when it is most needed to overcome theinertia ofthe parts and the frictional resistance, which under light loads is amaterial factor of inaccuracy. As the load increases, however, theincreasing current in the series coils operates with increasing effectupon the resultant field, which actuates the armature and diminishes orneutralizes this independent torque due to the diverter. Therefore thedevice, automatically, as it were, produces a starting torque when mostneeded and gradually loses it as there is less need for it. Thiseonduces to a speed that is in exact ratio to the watts, or, in otherwords, to the essentially regular or straight line characteristic of thepresent meter.

The meter herein described may be used in singlephase or two-phasealternating currents an d with primary or secondary circuits. In Fig. 0it is represented as measuring the energy of single-phase currents. Thecurrents supplied by the generator J are transformed for utility at j,from whence they pass through the field-coils in series and around thefield-core to the lamps or other translating devices J". The volt orshunt coil is excited by being placed in multiple upon the leads, asshown, and also connected in series with the inductance-coil and itsU-shaped core. In Fig. 7 the meter is connected into the primary circuitof the alternating-current dynamo or generator J and measures the totaloutput. The shunt-coil in this case is excited by a small transformer j,which reduces the primary electromotive force to a much lower orsuitable pressure, so that it can be used with safety. Aninductance-coil is also c011- nected in series with this secondarycircuit and shunt-coil to produce the necessary lag between the seriescoil energized by the primary circuit and the shuntcoil energized by itssecondary circuit. The primary current is used to supply thetransformerj with its lamps in a secondary circuit. In Fig. 8 the meteris adapted to operate on the three-wire system of distribution. Thisconsists of the two transfermer-primariesjj and their secondaries in, Z,and m, the line or circuit on representing the two inside terminals ofthe two transformers,or what is termed the neutral or third wire. Theouter wires 7.; and Z are connected around the two poles of thefield-cores, respectively, and thence to the lamps, and the volt orshunt circuit is connected across the two outside lines, which represent the sum of the electromotive forces of the two transformers, andin series with the ind uctance-coil.

To use this meter in integrating the energy on two-phase circuits ofdistribution, it may be connected up, as shown diagrammatically in Fig.5), wherein the series coils are 0011- nected in the commonreturn-circuit 7t" and the volt-coil across the two lines Z and m with anon-inductive resistance II in series with it, since this combinationdoes not require an impedance-coil to produce a lag, the necessarydisplacement of phase being maintained by the generator.

I do not intend to limit myself herein, in its relations to otherfeatures of myinvention, to the use of a shuntcore wound upon one endonly, or to a sh unt-core enlarged at one end and wound at the other, orto the position and arrangement of the shunt coil and core, nor,similarly, to a field-core provided with enlarged poles, or to theparticular form of the field-core, nor, likewise, to the specific formof inductive resistance described; neither do I limit myself to thespecific means set forth for producing the independent starting torquein conjunction with the shuntcoil, nor to the use of an imperforatearmature; but

\Yha-t I claim, and desire to secure by Letters Patent, is

1. The combination with the armature, of a field due to and varying withthe current in amperes flowing in the series coil, an asynphased fieldrepresenting the electromotive force in volts and varying directly asthe pressure, and means for inducing an independent torque between saidvoltage field and the armature.

2. The combination with the armature, of a field due to and varying withthe current in amperes flowing in the series coil, an asynphased fieldrepresenting the electromotive force in volts and varying directly asthe pressure, and means for diverting the flux of the latter field toinduce an independent torque on the armature.

3. The combination with the cylindrical armature, of field coils andcore inducing a field varying with the currentin amperes, a shunt orvolt coil and core inducing a field varying with the electromotive forcein volts, and a magnetizable diverter located opposite said shunt-coiland on the other side of the armature-shell.

4. The combination with the cylinder ar mature, of field-coils and coreinducing a field varying with the current in amperes, a shunt coil andcore inducing a field varying with the clectromotive force in volts, aparamagnetic diverter located opposite said shunt or volt coil and onthe other side of the armatureshell, and means for adjusting saiddiverter.

5. The combination with the cylindrical armature, of field coils andcore inducing a field varying with the current in am peres, a shunt coiland core axially at right angles to the axis of the field-coils andinducing a field varying with the electromotive force in volts, and amagnetizable diverter located opposite said shunt-coil and on the otherside of the armature-shell.

(3. The combination with the cylindrical armature, of field coils andcore inducing a field varying with the current in amperes, a shunt coiland core axially at right angles to the axis of the field-coils andinducing a field varying with the electromotive force in volts, amagnetizable diverter located opposite said shunt or volt coil and onthe other side of the armature-shell, and means for adjusting saiddiverter relatively to the axis of said shunt-coil.

7. The combination with the cylindrical armature, of field coils andcore external thereto and inducing a field varying with the current inamperes, a shunt coil and core inclosed within the armature and inducinga field varying with the electromotive force in volts, and amagnetizable diverter located opposite the volt-coil externally to thearmature.

8. The combination with the cylindrical armature, of field coils andcore external thereto and inducing a field varying with the current inamperes, a shunt coil and core inclosed within the armature and inducinga field varying with the electromotive force in volts, a magnetizablediverter located opposite the volt or shunt coil, externally to thearmature, and means for the adjustment of the proximate face of saiddiverter laterally in relation to the magnetic axis of said volt-coil.

9. The combination with the armature, and with a field-magnet, of ashunt-core and a shuntcoil wound upon one end of said core.

10. The combination with the arn1ature,and a field-magnet, of ashunt-core arranged with one end intersecting the axis of thefield-magnet, and a shunt-coil wound upon the opposite end only of saidcore.

11. The combination with the arn1ature,and with a field-magnet, of ashunt-core enlarged at one end, and a shunt-coil wound upon the smallerend thereof.

12. The combination with the ar1nature,and with a field-magnet, of ashunt-core enlarged at one end and arranged with said enlarged endintersecting the axis of said field-magnet, and a shunt-coilwound uponthe reduced end only of said shunt-core.

13. The combination with the armature of a field-core having anelongated yoke and insetting poles, field-coils wound upon said poles, ashunt-core, and a shunt-coil wound upon said shunt-core.

14. The combination with the armature of a fieldcore having an elongatedyoke and insetting poles, field-coils wound upon said poles, ashunt-core, and a shunt-coil wound upon one end only of said shunt-core.

15. The combination with the armature,of a field-core having anelongated yoke and insetting poles at opposite ends of a diameterthrough the armature, field-coils wound upon said poles, a sh unt-coreenlarged at one end, and a shunt-coil wound upon the smaller end of saidshunt-core.

16. The combination with the armature,ofa field-core having an elongatedyoke and insetting poles at opposite ends of a diameter through thearmature, field-coils wound upon said poles, a shunt-core enlarged atone end and arranged with said enlarged end between the poles of thefield-core, and a shunt-coil wound upon the smaller end of saidshuntcore.

17. The combination with the armature, of a field-core having anelongated yoke and insetting enlarged poles at opposite ends of adiameter through the armature, field coils wound upon the enlargedpoles, a shunt-core, and a shunt-coil wound upon one end only of saidshunt-core.

18. The combination with the armature,of a field-core having anelongated yoke and insetting enlarged poles at opposite ends of adiameter through the armature, field-coils wound upon the enlargedpoles, a shunt-core enlarged at one end, and a shunt-coil wound upon thesmaller end of said shunt-core.

19. The combination with the armature,ofa field-core having an elongatedyoke and insetting enlarged poles at opposite ends of a diameter throughthe armature, field-coils wound upon the enlarged poles, a shunt-coreenlarged at one end and axially at right angles to the axis of thefield-core, and a shuntcoil wound upon the smaller end of saidshunt-core.

20. The combination with the armature, of a field-core having anelongated yoke and -insetting enlarged poles at opposite ends of adiameter through the armature and external 20. The combination with thearmature,and

thereto, field-coils wound upon said enlarged poles, a shunt-coreenlarged at one end and located within the armature with its enlargedend between the poles of the field-core, and a shunt-coil wound upon thesmaller end of said shunt-core.

21. The combination with the armatu re, of a field-core having anelongated yoke and insetting enlarged poles at opposite ends of adiameter through the armature and external thereto, field-coils woundupon said enlarged poles, a shunt-core enlarged at one end and locatedwithin the armature axially at right angles to the axis of thefield-coils, and a shunt-coil wound upon the smaller end of said core.

22. The combination with the armature, and with the field-coils, of theshunt-coil with its iron core, reduced at the end upon which the coil iswound, and an inductive resistance in the shunt-circuit, adapted topermit a flow of current varying with the electromotive force.

23. The combination with the armature,and with the field-1n agnet, of ashunt-core inclosed within said armature, a shun t-coil wound upon oneend only of said core, and an inductive resistance in the shunt-circuitadapted to permit a flow of current varying with the electromotiveforce.

24. The combination with the armature,and with the field-core havingenlarged inturned poles and field-coils wound upon said poles, of theshunt-core enlarged at one end, the shunt-coil wound upon the smallerend of said core, and the inductance-coil with its laminated U-shapedcore, connected in series in the shunt-circuit.

25. The combination with the arn1atnre,an d shunt core and coil, of amagnetizable diverter pivotally adj ustable with reference to the axisof said core and coil, and means whereby said diverter may be adjustedbodily and laterally.

shunt core and coil, of a magnetizable diverter adjustable in and outwith reference to the periphery of saidarmatnre.

27. The combination with the armature and shunt core and coil, of a 1nagnetizable diverter adjustable in and out with reference to theperiphery of said armature, and means for its lateral adjustment alongsaid periphery.

98. The combination with the armature,a1nl shunt coil and core, of amagnetizable diverter adjustable pivotally and also in and out withreference to the periphery of the armature, and means for its bodily andlateral adjustment along said periphery.

29. The combination with the meter-spindle, of the cylindrical armaturecarried thereby, the fixed sleeve encircling said spindle within thearmature and supported from the meter-frame, the iron corc-punchingsbuilt upon said sleeve to form a shunt-core, and the shunt-coil woundupon said punchings.

30. The combination with the meter-spindle, of the cylindrical armaturecarried thereby, the fixed sleeve encircling said spindle and supportedfrom the 1neter-irame,the corepunchings built upon the upper line ofsaid sleeve within the armature, the shuntcoil wound upon the core thusformed, the adj ustable arm supported upon the lower line of saidsleeve, and the magnetizable diverter carried at the outer end of saidarm.

31. The combination with the field and sh uut coils, of a closed-circuitarmature and means for its adjustment into or out of the field.

In testimony that I claim the foregoing as my invention I aifix mysignature, in presence of two witnesses, this 21st day of April, 1 D.1806.

THOMAS DUNCAN.

Witnesses:

HENRY W. CARTER, Jonx E. DALTON.

